The present invention relates to an insulating adhesive for electronic parts, which is useful for bonding lead frames to semiconductor chips (chips) in the production of semiconductor devices, particularly LOC (Lead On Chip) or COL (Chip On Lead) semiconductor devices, and also to a lead frame and a semiconductor device using the same.
To meet the scaling up of semiconductor chips, LOC (Lead On Chip) and COL (Chip On Lead) structures have recently been employed for packaging semiconductor devices. In LOC structures, insulation resin film bearing insulating adhesive layers has been used to bond inner leads to chips. To produce such semiconductor devices, first an insulation resin film bearing insulating adhesive layers is produced and punched with metal molds to stick it to a lead frame. A semiconductor chip is then mounted on the lead frame with heat and pressure. The chip and the lead frame, in general, are connected by bonding wires, such as gold wires, and sealed with resins.
Such semiconductor devices using the insulation resin film bearing insulating adhesive layers suffer from the flash formed on punching and the poor yield factor of the insulation resin film due to the extremely little area used actually, and are also subject to package-cracking during solder reflow for mounting them on substrates due to the hygroscopicity of the materials of the insulation resin film.
The object of the present invention is to provide an insulating adhesive for electronic parts useful for bonding semiconductor chips to lead frames in the production of semiconductor packages using no insulation resin film, a lead frame and a semiconductor device using the insulating adhesive for electronic parts.
The present invention provides an insulating adhesive for electronic parts (hereinafter may be abbreviated to xe2x80x9cinsulating adhesivexe2x80x9d), which is to be used for bonding a semiconductor chip to a lead frame and comprises a resin and a solvent, wherein the resin having
(A) a weight average molecular weight (Mw) of 30,000 to 300,000 based on conversion into polystyrene and
(B) a ratio of weight average molecular weight (Mw)/number average molecular weight (Mn) of 5 or less, and
(C) the insulating adhesive for electronic parts having a viscosity of 5,000 to 100,000 mPa.s at a rotation number of 10 rpm and a viscosity ratio (xcex71 rpm/xcex710 rpm) of 1.0 to 6.0 as measured at 25xc2x0 C. with an E-type viscometer.
When applied to a lead frame, the insulating adhesive for electronic parts of the present invention preferably comes in contact with the lead frame at a contact angle of 20 to 130xc2x0 and at an aspect ratio of 0.05 to 2.0 before drying, and, after drying, at an aspect ratio of 0.005 or more.
When applied to a lead frame, dried and then forced to absorb moisture, the insulating adhesive for electronic parts of the present invention preferably foams at 200xc2x0 C. or more.
When applied to a lead frame, dried and then forced to absorb moisture, the insulating adhesive for electronic parts of the present invention preferably has a glass transition temperature of 100 to 250xc2x0 C.
The present invention further provides a lead frame, which bears an adhesive layer formed by applying the insulating adhesive for electronic parts of the present invention to the lead frame and then drying.
The present invention further provides a semiconductor device comprising a lead frame and a semiconductor chip, the lead frame and the semiconductor chip being bonded together with the insulating adhesive for electronic parts of the present invention.
In a preferred embodiment of the semiconductor device according to the present invention, the lead frame bears an adhesive layer formed by applying the insulating adhesive for electronic parts to the lead frame and then drying, and the semiconductor chip is bonded to the lead frame with the adhesive layer.
In another preferred embodiment of the semiconductor device according to the present invention, 0.05 to 20% area of a surface of the semiconductor chip is in contact with the insulating adhesive for electronic parts.
In another preferred embodiment of the semiconductor device according to the present invention, inner leads of the lead frame are placed over a main circuit surface of the semiconductor chip and are connected to an electrode pad on the semiconductor chip with metal wires, the semiconductor chip, the inner leads and the metal wires are sealed with a sealing material, and at least two of the inner leads are bonded to the semiconductor chip with the insulating adhesive for electronic parts.
In another preferred embodiment of the semiconductor device according to the present invention, inner leads of the lead frame are placed over a main circuit surface of the semiconductor chip and are connected to an electrode pad on the semiconductor chip with metal wires, the semiconductor chip, the inner leads and the metal wires are sealed with a sealing material, power supply inner leads are bonded to the semiconductor chip with the insulating adhesive for electronic parts, signal transmission inner leads are not bonded to but kept apart from the semiconductor chip, and the signal transmission inner leads are separated from the main circuit surface of the semiconductor chip farther than the power supply inner leads are.